As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option is an information handling system. An information handling system generally processes, compiles, stores, or communicates information or data for business, personal, or other purposes. Technology and information handling needs and requirements can vary between different applications. Thus information handling systems can also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information can be processed, stored, or communicated. The variations in information handling systems allow information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems can include a variety of hardware and software resources that can be configured to process, store, and communicate information and can include one or more computer systems, graphics interface systems, data storage systems, networking systems, and mobile communication systems. Information handling systems can also implement various virtualized architectures. Data and voice communications among information handling systems may be via networks that are wired, wireless, or some combination.
An information handling system typically requires power to operate. Such power is supplied by a power supply unit (PSU). To provide clean, stable power, a PSU typically includes a bulk capacitor, such as an electrolytic capacitor, to serve as a reservoir of electric charge. Such a reservoir can accept additional charge beyond that drawn for use by the various elements of the information handling system and can provide charge drawn by the elements of the information handling system during brief disruptions of the input power received by the PSU. The period of time during which a PSU can continue to provide power to the elements of the information handling system without itself being supplied with input power is known as the hold up time.
If input power is disrupted for a substantial portion of the hold up time, the amount of charge stored in the reservoir is reduced by the power that continues to be supplied to the elements of the information handling system. When input power is restored to the PSU, a depleted reservoir can draw a large amount of current to refill itself with charge. Such current can be referred to as resumed inrush current, as it rushes in when the normal operation is resumed by the restoration of input power.
Large resumed inrush current may overload components used to handle the supply of current and can trigger over current protection, such as tripping a circuit breaker (e.g., an alternating current (AC) circuit breaker). The tripping of a circuit breaker or the failure of a component from too much current can cause the unexpected stoppage or failure of an information handling system.
Another type of inrush current is initial inrush current, which occurs when power is initially applied to a PSU. As the reservoir, such as a bulk capacitor, is initially empty, it initially tends to draw a large amount of initial inrush current. It is possible to add a resistor or a temperature-sensitive device, such as a positive temperature coefficient (PTC) or negative temperature coefficient (NTC) resistor, in series with and before a bridge diode to limit the initial inrush current based on power dissipation of the temperature-sensitive device resulting from the initial inrush current. However, it can be undesirable to have the resistor or temperature-sensitive device in the circuit during normal operation after the brief initial inrush current has subsided, so the additional cost and complexity of another device, such as a relay across the temperature-sensitive device, is typically incurred to bypass the resistor or temperature-sensitive device during normal operation.
However by bypassing the resistor or temperature-sensitive device, the circuit is unprepared to respond to resumed inrush current during brief disruptions of input power during normal operation. If the alternating current (AC) line drops out and then resumes, high AC resumed inrush current can occur and can be greater than the initial inrush current if a current limiting PTC/NTC resistor is still bypassed by a relay.
While a typical hold up time may be, for example, 10 mS, a PSU designed to provide a longer hold up time can exacerbate inrush current problems, as the amounts of energy depleted from the reservoir over the longer hold up time can be greater. As examples, a hold up time of 20 mS according to an Information Technology Industry Council (ITI) curve and a hold up time of 30 mS for a special feature set may bring risks, such as triggering AC breaker over current protection unexpectedly if several PSUs are in parallel and damaging input devices such as a fuse, a bridge diode, and a power factor correction (PFC) bypass diode. If a PFC bypass diode is rated for 3A of forward current, a 600V peak reverse voltage, it may have a maximum surge forward current of, for example, 100A. The maximum surge forward current is typically limited to short duration, such as a non-repetitive half cycle of the AC sine wave it is rectifying. However, the magnitudes of current typically associated with inrush currents, which can exceed, for example, 100A, can result in failures of PFC bypass diodes.